Say you want to delete a rule in your uncomplicated firewall (ufw). You run
ufw help and see that the entry for delete is
delete RULE|NUM delete RULE
But when you check the status with
sudo ufw status, all you see is this
Status: active To Action From -- ------ ---- OpenSSH ALLOW Anywhere 443 ALLOW Anywhere OpenSSH (v6) ALLOW Anywhere (v6) 443 (v6) ALLOW Anywhere (v6)
Where's the rule number?
What you need is
sudo ufw status numbered, which has the rule number in the left hand column.
Status: active To Action From -- ------ ---- [ 1] OpenSSH ALLOW IN Anywhere [ 2] 443 ALLOW IN Anywhere [ 3] OpenSSH (v6) ALLOW IN Anywhere (v6) [ 4] 443 (v6) ALLOW IN Anywhere (v6)
So if you want to delete your OpenSSH rule for IPv6, you know to run
sudo ufw delete 3.